Quadrature pulse-width modulation methods and apparatus

Abstract

Switched-mode amplifiers and devices having such amplifiers include quadrature pulse-width modulation that is based on cartesian (as opposed to polar) coordinates. Two sets of pulses that represent respective in-phase and quadrature components of a conventional cartesian-coordinates input signal can be combined such that the combined set of pulses can be provided to a switched-mode amplifier without nonlinear cartesian-to-polar transformation and its associated wider internal bandwidth and other problems.

1. A device for generating quadrature pulse-width modulation (QPWM) signals, comprising:
 a circuit configured to generate, based on an in-phase (I) component and a quadrature phase (Q) component of an input signal, at least two respective pulse-width modulated (PWM) signals that are trains of pulses; and 
 a reshaper configured to transform the at least two PWM signals into a QPWM signal, wherein the QPWM signal is a succession of pulses, and alternating pulses have widths that correspond to one or the other of the I and Q components; 
 wherein the circuit comprises a first pulse-width modulator configured to generate one of the PWM signals based on the I component and a second pulse-width modulator configured to generate another of the PWM signals based on the Q component, each of the first and second pulse-width modulators comprises a respective pair of controllable time-delay elements and a logic gate, each of the pairs of controllable time-delay elements phase-shift a reference signal in opposite temporal directions based on a respective one of the I and Q components, and each gate produces a respective one of the PWM signals based on the phase-shifted reference signal. 
 
     
     
       2. The device of  claim 1 , wherein at least one of the first and second pulse-width modulators includes a pair of comparators and an inverter. 
     
     
       3. The device of  claim 1 , wherein each of the first and second pulse-width modulators comprises a respective low-pass filter and a differential amplifier configured to combine a fed-back portion of the respective PWM signals and a respective one of the I and Q components. 
     
     
       4. The device of  claim 3 , further comprising at least one predistorter that produces at least one of the I and Q components on which respective PWM signals are based. 
     
     
       5. The device of  claim 1 , wherein the reshaper includes a logical OR gate that produces the QPWM signal based on signals from the logic gates. 
     
     
       6. The device of  claim 1 , wherein the I and Q components are differential signals, and the reference signal is a square wave. 
     
     
       7. The device of  claim 1 , wherein the I and Q components are differential signals, and the reference signal comprises first and second rectangular waves that have different duty cycles. 
     
     
       8. The device of  claim 1 , wherein the reshaper includes at least two logic gates that produce the QPWM signal based on signals from the at least two PWM signals. 
     
     
       9. A device for generating quadrature pulse-width modulation (QPWM) signals, comprising:
 a circuit configured to generate, based on an in-phase (I) component and a quadrature phase (Q) component of an input signal, at least two respective pulse-width modulated (PWM) signals that are trains of pulses; and 
 a reshaper configured to transform the at least two PWM signals into a QPWM signal, wherein the QPWM signal is a succession of pulses, and alternating pulses have widths that correspond to one or the other of the I and Q components, and the reshaper includes two pairs of logic gates and a NAND gate for each pair that produce the QPWM signal based on signals from the pairs of logic gates. 
 
     
     
       10. A device for generating quadrature pulse-width modulation (QPWM) signals, comprising:
 a circuit configured to generate, based on an in-phase (I) component and a quadrature phase (Q) component of an input signal, at least two respective pulse-width modulated (PWM) signals that are trains of pulses; 
 a reshaper configured to transform the at least two PWM signals into a QPWM signal, wherein the QPWM signal is a succession of pulses, and alternating pulses have widths that correspond to one or the other of the I and Q components; 
 at least two amplifiers, wherein the QPWM signal comprises a pair of QPWM signals and each of the pair of QPWM signals is amplified by a respective amplifier, and a combiner configured to combine the amplified pair of QPWM signals. 
 
     
     
       11. The device of  claim 10 , further comprising a demodulator configured to produce feedback signals based on a combined signal produced by the combiner, wherein the PWM signals are based on combinations of the feedback signals and the I and Q components. 
     
     
       12. A method of generating quadrature pulse-width modulation (QPWM) signals, comprising the steps of:
 converting, by a converting circuit, in-phase (I) and quadrature (Q) components of an input signal into at least two pulse-width modulated (PWM) signals that are trains of pulses, and 
 reshaping, by a reshaping circuit, the at least two PWM signals into a QPWM signal, wherein the QPWM signal is a succession of pulses, and alternating pulses have widths that correspond to one or the other of the I and Q components, and the QPWM signal comprises a pair of signals; 
 separately amplifying each of the pair of signals; and 
 combining the amplified pair of signals. 
 
     
     
       13. The method of  claim 12 , wherein the converting step comprises combining fed-back portions of the PWM signals and respective ones of the I and Q components to be converted. 
     
     
       14. The method of  claim 13 , wherein the converting step further comprises predistorting the I and Q components. 
     
     
       15. The method of  claim 12 , further comprising adding feedback signals based on the combined amplified pair of signals to respective ones of the I and Q components.